This invention relates to optical switches that rely upon semiconductor action.
Many types of optical switches have been proposed within the last 15 years, including switches based on temperature changes, refractive index changes, applied magnetic and/or electrical fields, and other environmental changes. Most of these structures are complex, requiring multiple layers of opto-electronic or semiconductor materials that are switched between two or more states using complex control mechanisms. Further, most of these systems provide only two states, fully on and fully off, and do not provide for controllable partial transmission of the light.
What is needed is a simpler system for switching light that does not depend upon a multi-layer opto-electronic or semiconductor material and that provides full, partial or zero transmission of incident light, controlled by a single gate voltage value. Preferably, the gate voltage difference between a substantially fully transmissive state and a fully absorptive state should be large enough
These needs are met by the invention, which uses a simple MIS semiconductor system and an electrical field source to controllably absorb or transmit light having a selected wavelength xcex or range of wavelengths that is received at the semiconductor. A gate voltage Vg is applied in a selected direction (transverse) relative to the direction of propagation of light parallel to a gate-insulator-semiconductor interface. In a first state, the gate voltage Vg is much less than the gate voltage threshold Vg(thr) required for semiconductor inversion near the gate (including Vg=0). Substantially full transmission of light parallel to the interface occurs in the first state. In a second state, the gate Vg is approximately equal to Vg(thr), being somewhat less than or somewhat greater than the inversion threshold. As Vg is increased within this voltage range, light transmission varies from a high value (≈70-90 percent) to nearly 0 percent. In a third state, the gate voltage Vg is much greater than Vg(thr), and light transmission in this third state is substantially zero. The light transmission percentage is controlled by a fraction of sub-band carriers (holes or electrons) that accumulate near the insulator-semiconductor interface and that are available to absorb photons of energy E=hc/xcex from the incident light.